1. Field of the Disclosure
This disclosure relates generally to apparatus and methods for stimulating operations for the production of hydrocarbons using injection of fluids that include a selected amount of nano heat transfer elements therein.
2. Background of the Art
Wellbores are drilled in subsurface formations for the production of hydrocarbons (oil and gas). Modern wells can extend to great well depths, often more than 15,000 feet. Some hydrocarbon producing zones in the earth subsurface include heavy oil (high viscosity oil) and bitumen trapped in formation with relatively low mobility. An oil bearing zone also is referred to herein as a “reservoir”. Secondary operations are often performed to facilitate the flow of oil through such reservoirs. Secondary operations may include hot water injection, cyclic steam stimulation (CSS), continuous steam injection or steamflooding, steam assisted gravity drainage (SAGD), steam and gas push (SAGP), expanded solvent SAGD (ES-SAGD) and the like. In the cyclic steam stimulation process, a limited amount of steam is injected into the reservoir through the well. The injection period generally lasting one to three weeks is followed by a soaking period of few days during which time the well is shut in to allow heat transfer from the condensing steam to the reservoir fluids and the rock. Finally, the formation fluid is allowed to flow back to the well naturally, which fluid is then pumped to produce hydrocarbons. Production period usually lasts from half a year to one year per cycle. In the CSS process, several (two to three) cycles are performed in the same well, each cycle including injecting fluid and producing formation fluid. In the continuous steam injection process, steam is continuously injected into one or several wells and the formation fluid (oil) is driven to separate production wells. The injection and production wells may be vertical, deviated or horizontal wells. In the SAGD gravity drainage, steam is injected in a horizontal well located a few meters above a horizontal production typically placed or formed near the bottom of the reservoir. Steam has a tendency to rise forming a heated steam chamber while the condensate and warmed oil fall toward the production well. The unique feature of SAGD is the use of gravity as the primary force for moving oil through the formation. The efficiency of SAGD may be enhanced by adding a small amount of non-condensable gases, such as natural gas or nitrogen to steam during the middle or the late stage of the SAGD process (steam and gas push method) or by injecting a solvent in the vapor phase together with steam (ES-SAGD). Thus, in these secondary operations, generally referred to as hot fluid injection processes, heated steam is pumped into the reservoir proximate to a production well drilled into the reservoir, which well may be a vertical, deviated or horizontal well. The hot fluid heats the oil in the reservoir, reduces its viscosity, and enables it to flow from the formation into the well, from which the oil is produced to the surface. In hot fluid injection operations, heat is transferred from the injected fluid to the rock and naturally occurring fluids, including hydrocarbons, in the reservoir. The hot fluid injection applications require great amounts of hot fluids. The effectiveness of such injected fluids (steam, hot water or hot solvent) for stimulation operations depends on the heat capacity of the injected fluid. It is therefore desirable to increase the heat capacity of the fluids utilized for such stimulation applications.
The disclosure herein provides apparatus and methods that increase the heat capacity of the injection fluids by adding heated heat transfer elements or particles in a base fluid and wherein the heat transfer elements transfer heat to the fluid in the formation in addition to the heat transferred by the fluid itself. In one aspect, the heat transfer elements may include nano elements, micro elements or a combination thereof, which elements include a solid shell and an inner core that may melt or undergo another phase transition above a certain temperature.